Studies On The Structure And Growth Mechanism Of Nm-sized Metallic Atomic Islands On Liquid Substrates

Silver (Ag) and Copper (Cu) nm-sized atomic islands, performed on the liquid (silicone oil) substrate surfaces by vapor phase deposition method, have been fabricated successfully at room temperature. Based on the optical microscope, etc, surface morphology, microstructure, material density and aggregation mechanism of the atomic islands have been studied systematically.It is found that the aggregation processes of the Ag and Cu nm-sized atomic islands approximately satisfy the two-stage growth model, which is similar to that of the other metallic island (Au, Al, Fe, Ni, etc.) systems on the silicone oil surfaces. The experimental results show that, for the nominal film thickness h is smaller than the critical thickness hc, the apparent Ag coverage of the total area, namely p, increases linearly with h and satisfies p= kh. For h> hc, however, the coverage p decreases with h firstly and then exhibits fluctuation behavior. It is clear that the aggregation mechanism changes dramatically with the increase of the nominal film thickness. In addition, as h increases from 0.2nm to 2.0 nm, transmission electron microscope (TEM) measurements show the transformation of the amorphous structure to polycrystalline structure of the islands and the corresponding material density 3 of the islands increases from 45% to 70%. These results above suggest that it is feasible and reliable to study the microstructures and aggregation mechanism of the atomic islands during the growth process of the islands via the simple experimental method.For the different deposition flux f(0.05<f< 0.30 nm/s) and h< hc, it is found that the surface coverage p decreases with f.In addition, the dependence between p and h satisfies p=kh. The slope k decreases with f and the ratio of the maximum slope kmax to the minimum kmin is about 2. Atomic force microscope (AFM) measurements show that the average height HAFM of the islands increases gradually with f and the ratio of the maximum (HAFM)max to minimum (HAFM)min equals around 2, which is in good agreement with the result kmin/kmax≈1/2. The results indicate that the surface morphology, microstructure and aggregation mechanism strongly depend on the deposition flux f,which is confirmed by the theoretical analysis.According to the two-stage growth model, the branched islands are composed of the compact islands due to the collision and adhesion to each other of the compact islands. During the process of the collision, it is found that, the velocity of the islands increases rapidly as the distance w between two compact islands is smaller than the critical distance wc. Further analysis shows that the oil surface around the islands should be uneven, which could introduce long range force F and make contributions to the cohesion of the compact islands. The long range force F is of the order of 10"4 N, which is far more than the 10"12 N of the van der Waals force.For the Cu atomic islands with h=0.4 nm, which was kept in the evaporation chamber (in vacuum condition) for time period At= 13 min and then removed from the chamber. During the capture time t= 0-120 min, the Cu atomic islands growth and their surface morphology evolves clear gradually; for t> 120 min, the surface morphology of the islands remains nearly unchanged. AFM measurements show that the atomic islands are composed of atomic grains and the average height HAFM of the islands increases from 7±1 to 13±1nm with t. The mean diameter of the Cu atomic granules remains nearly unchanged (about 30 nm). In the meanwhile, TEM measurements display that polycrystalline structures of the Cu atomic islands remain unchanged during the evolution process. The phenomenon suggests that the granules squeeze each other during the evolution processes and some of them are heightened. Therefore, average height of the islands increases gradually and the morphology of the islands becomes more clearly. In addition, the surface morphology and microstructure of the Cu islands depend on the nominal film thickness and deposition flux.The doctoral dissertation is arranged as following:In chapter I, a brief review of the atomic-scale study of kinetics in film growth on solid substrates is given; the studies of the aggregation behavior of the granules on the surfaces of water and in some liquid are introduced; finally, the researches of the surface morphology, formation mechanism, microstructure and physical characteristics of the thin films forming on the silicone oil surfaces is presented systematically.In chapter II, the surface morphology, the material density and formation mechanism of the Ag nm-sized atomic islands fabricating on the silicone oil surfaces are introduced. In addition, the dependences between the aggregation process and nominal film thickness, deposition flux are studied. In the meanwhile, the long range force between the adjacent compact islands is revealed.In chapter III, the morphology and microstructure evolution of Cu atomic islands on silicone oil surfaces in ambient atmosphere are studied systematically.Ia chapter IV, the main conclusions and prospects are given.